This apparatus is directed to a device to be placed in a drill stem at the time that the drill stem is pulled from the well borehole during drilling and, more particularly, is a device for weighting the column of mud in the drill stem.
During drilling of a well, it is necessary to periodically removed the drill stem from the borehole, typically to replace the drill bit. When this occurs, the drill stem is normally lifted up and disassembled joint by joint or perhaps stand by stand. In the process of removing the pipe from the borehole, it is normally lifted in a wet condition and, upon unthreading, may spill drilling fluid on the rig floor creating a risky condition. Moreover, this destroys the hydrostatic balance which existed in the borehole. Heretofore, this has been overcome by slugging the column of mud in the drill stem with a slug of drilling fluid of heavier density so that it will tend to keep the level of mud down in the drill pipe due to the hydrostatic unbalance created. This requires use of different type material in the drilling fluid such as the use of an oil base mud when the column of mud otherwise located in the borehole is a clay based mud. Mixing the two is undesirable. Sometimes as in the case of oil base mud systems it is necessary to remove the weight materials used to obtain the mud balance required for drilling.
Various and sundry devices have been provided heretofore and representative devices are disclosed in patents 2,578,900, also 2,633,202 and 3,276,520. The latter shows a set of resilient cups while the older of these references shows modified cups having overlips. The intermediate reference sets forth a sleeve. The several references however do not set forth a device which is so aptly able to pass through internal upset pipe which requires a narrowing of the tool on each occasion of encountering the internally constructed shoulders located at the tool joints.
The present apparatus discloses an elongate member which is buoyantly carried on the top of the mud column in the drill stem as it is being pulled and which includes a central elongate mandrel. The mandrel is of relatively narrow diameter to receive thereon a telescoped and slidable resilient sleeve. The resilient sleeve is not shaped as a cup, but rather incorporates upper and lower ends which are relatively narrow and are mounted on circular rings to enable telescoping movement of each end independently on the mandrel. The sleeve bows outwardly at the central portions and defines a resilient wiping surface. This surface is able to pass through the internal upset pipe. When it does, the sleeve is constricted only slightly, forcing the two ends farther apart, but they are both free to move. The two ends of the sleeve are arranged in a circular construction around the mandrel. Conveniently, shoulders at the upper and lower ends of the sleeve supported by the mandrel define the control sleeve position, but such movement is nevertheless permitted during transition through an internal upset. The transition thus occurs as the device is traveling through the drill stem and yet permits the sleeve to slide through the internal upset, shrinking at the fatter central portion, forcing the two ends thereof relatively apart, and moving at one end or the other to accommodate the appropriate elongation on diametric shrinkage, and further restoring to the original shape after transition through the internal upset. This is markedly different from cups which face upwardly or downwardly. Likewise, it is different from sleeves of substantially uniform diameter, and is substantially different from the wiping action provided by such devices.
One modification of the present apparatus is the incorporation of a split ring defining a plurality of independent collet fingers arranged around a tapered surface. This is located at the upper portions of the tool to thereby define a slip assembly which blocks upward movement of the tool in the event of a blowout. This functions in conjunction with the resilient or wiping rubber just mentioned, and is able to hold against specified levels of upward pressure transmitted through the column of mud in the drill stem to the present apparatus. There is in addition to that an axial passage through the tool which enables drilling mud to be pumped down through the tool, entering the tool at the upward end and travelling axially along the length of the mandrel in the interior and passing out through the bottom of the tool. This path is made exclusively one way by incorporation of a check valve in the pathway. That extends through the mandrel which is in the turn supportive of the sleeve mentioned above.
The foregoing briefly sets out certain aspects of the present disclosure, but details of the present apparatus will become more readily apparent and understood in conjunction with the drawings of the preferred embodiment, and it is therefore a structure including the components illustrated discussed below for the preferred embodiment.